Independent assortment describes how...

• A. Independent assortment randomizes inheritance of different genes on different chromosomes; linked genes tend to be inherited together unless crossing over occurs.
• B. All genes are inherited together as a single unit.
• C. Genes on the same chromosome always assort independently.
• D. Crossing over prevents any variation.

Answer: (A)

Independent assortment describes how alleles for different genes are sorted into gametes independently during meiosis, especially for genes on different chromosomes. When homologous chromosome pairs line up and separate, the maternal or paternal chromosome copy for each gene is distributed to gametes without regard to the others, producing many different allele combinations in offspring. This is why genes on separate chromosomes can assort independently, increasing variation in the next generation.

Linked genes—those close together on the same chromosome—tend to be inherited together because they travel as a unit, unless crossing over during meiosis occurs to shuffle them and create new combinations. The other ideas—genes all inherited as one unit, or that genes on the same chromosome always assort independently, or that crossing over prevents variation—don’t fit the actual mechanism.